Abstract

We applied anisotropic stress to LaMnO3+δnanoparticles synthesized in one-dimensional pores of mesoporous silica and investigated the effects of the anisotropic strain on the nanoparticles, which consisted of ferromagnetic and antiferromagnetic particles. The nanoparticles in the one-dimensional pores were crushed without stress in the direction parallel to the silica walls that separated the pores when the mesoporous silica containing the nanoparticles is pressurized. X-ray diffraction patterns of the nanoparticles indicated that the lattice strain increased with increasing applied pressure. The lattice constants were found to reduce anisotropically, and the values saturated above a critical strain. Both the ferromagnetic and antiferromagnetic transition temperatures for the LaMnO3+δnanoparticles initially increased with increasing pressure and then remained constant at around the critical strain. These results indicate that anisotropic stress causes distortion of the shape of nanoparticles. This induces an increase in the lattice strain and the anisotropic compression of the crystal structure, which, in turn, results in an increase in the transition temperatures.

Received 30 May 2011Accepted 12 July 2011Published online 19 August 2011

Acknowledgments:

The synchrotron radiation experiments were performed at the beamline BL-8B in the Photon Factory (Proposal No. 2009G529). This work was supported by Grant-in-Aid for Scientific Research on Priority Areas (Grant No. 19052006) from the MEXT of Japan.